1. Field of the Invention
The present invention relates to a suction nozzle for holding electric components (including electronic components) by suction under a negative or reduced pressure (under vacuum), a method of detecting the position of the electric component as held by the suction nozzle, a method of detecting a bending of a suction pipe of the suction nozzle, a method of determining the angular position of the suction nozzle, a method of compensating the angular position of the suction nozzle, and a device arranged to handle the electric components.
2. Discussion of Related Art
For instance, a suction nozzle is used in an electric-component mounting system arranged to mount electronic components and other electric components on printed-wiring boards. In this instance, the suction nozzle is moved relative to an electric-component supply device and the printed-wiring board, for receiving the electric components from the electric-component supply device, and is operated to mount or place the electric components on the printed-wiring board. Generally, an image of the electric component held by suction by the suction nozzle is taken during a movement of the electric component from the electric-component supply device to the printed-wiring board, to detect the position of the electric component (as held by the suction nozzle) relative to the suction nozzle holding the electric component (hereinafter referred to as “hold position of the electric component”). Where the position to which the suction nozzle is moved is defined with respect to an axis of a nozzle holder which holds the suction nozzle, for example, the hold position of the electric component is defined as a relative position between the center of the electric component in a plane perpendicular to the axis of the nozzle holder, and the axis of the nozzle holder. Where the suction nozzle is adapted to hold the electric component such that the center of the electric component is aligned with the axis of the nozzle holder, the relative position between the center of the electric component and the axis of the nozzle holder represents an error of the hold position of the electric component held by the suction nozzle. If the error of the hold position of the electric component is detected, the hold position is compensated to eliminate the error, so that the electric component can be mounted on the printed-wiring board, as required.
From the standpoint of detecting the hold position of the electric component, it is desirable that an image of each electric component as held by the suction nozzle be taken while the electric component is held stationary with respect to an image-taking device. In this case where each electric component is stopped for taking its image, however, the required time from the moment at which the electric component is sucked to the moment at which the electric component is mounted on the printed-wiring board is inevitably increased, so that the efficiency of mounting of the electric components on the printed-wiring boards is accordingly lowered. In view of this drawback, it may be considered to take the image of the electric component without stopping the electric component, that is, while the electric component is in the process of moving. Where a nozzle moving device provided to move the electric components uses servomotors as the drive device, for example, the image of each electric component as held by the suction nozzle is taken by activating a strobe light or opening a shutter of the image-taking device, at the moment when the angles of rotation of the servomotors as detected by encoders have increased to predetermined values at which the suction nozzle is brought to a predetermined image-taking position at which the axis of the nozzle holder is located at the center of an imaging area of the image-taking device, for instance.
In the case indicated above, however, the image of the electric component is not necessarily taken when the axis of the nozzle holder is actually located at the center of the imaging area of the image-taking device. Where the image-taking device is activated when the outputs of the encoders have reached the predetermined values, for instance, there generally arises a delay between the moment at which the outputs of the encoders have reached the predetermined values and the moment at which the image of the electric component is actually taken by the image-taking device, so that the image of the electric component is taken when the axis of the nozzle holder is actually located apart from the center of the imaging area of the image-taking device. However, the hold position of the electric component held by the suction nozzle is calculated on an assumption that the axis of the nozzle holder is aligned with the center of the imaging area of the image-taking device, so that the error of the hold position as calculated includes a deviation of the axis of the nozzle holder from the center of the imaging area, resulting in deterioration of the accuracy of detection of the hold position of the electric component. The amount of the deviation of the axis of the nozzle holder with respect to the center of the imaging area increases with an increase in the speed of movement of the suction nozzle (nozzle holder), so that the amount of this deviation can be reduced by reducing the speed of movement of the suction nozzle. However, the reduction of the speed of movement of the electric component results in an increase in the time required for moving the electric component from the electric-component supply device to the printed-wiring board, and consequent reduction in the efficiency of mounting of the electric component.